Ventilation grille



FIG. 1 is a perspective view of the ornamental design for a ventilation grille.

FIG. 2 is a plan view thereof.

FIG. 3 is a bottom view thereof, the top view being identical; and,

FIG. 4 is a left side view thereof, the right side being identical. 

The ornamental design for a ventilation grille, as shown and described. 